1. Field of the Invention
The invention generally relates to the fabrication of integrated circuits and a method for depositing metal layers by chemical vapor deposition.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) integrated circuits. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on processing capabilities. The multilevel interconnect features that lie at the heart of this technology require careful processing of high aspect ratio features, such as vias, lines, contacts, interconnects, and other features. Reliable formation of these features is very important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, i.e., 0.25 xcexcm or less, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios of the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling sub-micron structures where the aspect ratio exceeds 4:1, and particularly where it exceeds 10:1. Therefore, there is a great amount of ongoing effort being directed at the formation of void-free, sub-micron features having high aspect ratios.
Conducting metals such as aluminum and copper are being used to fill sub-micron features on substrates during the manufacture of integrated circuits. However, aluminum and copper can diffuse into the structure of adjacent dielectric layers, thereby compromising the integrity of the devices being formed. Diffusion, as well as interlayer defects, such as layer delamination, may be prevented by depositing a liner layer, a barrier layer, or a combination of both, in a feature before depositing the conducting metal. The liner layer is conventionally composed of a refractory metal that provides good adhesion to the underlying material. The barrier layer is deposited on the liner layer or underlying material and is often a nitride of a refractory metal that prevents interlayer diffusion and minimizes chemical reactions between underlying materials and subsequently deposited materials.
With the recent progress in sub-quarter-micron copper interconnect technology, metals such as tantalum, niobium, tungsten, and the respective metal nitrides have become popular liner and barrier materials in copper applications. Depending on the application, a liner adhesion layer and/or a diffusion barrier layer may comprise a metal, such as tantalum, niobium, or tungsten, a metal nitride layer, such as tantalum nitride, niobium nitride layer, or tungsten nitride, a metal and metal nitride stack, or other combinations of diffusion barrier materials. Metal and metal nitride layers have been traditionally deposited by physical vapor deposition (PVD) techniques. However, traditional PVD techniques are not well suited for providing conformal coverage on the wall and bottom surfaces of high aspect ratio vias and other features. Therefore, as aspect ratios increase and device features shrink, new deposition techniques are being investigated to provide conformal coverage in these device features.
One proposed alternative to PVD deposition of metal and metal nitride layers is depositing the layers by chemical vapor deposition (CVD) techniques to provide good conformal coverage of substrate features. The ability to deposit conformal metal and metal nitride layers in high aspect ratio features by the disassociation of organometallic precursors has gained interest in recent years due to the development of metal organic chemical vapor deposition (MOCVD) techniques. In such techniques, an organometallic precursor comprising a metal component and organic component is introduced into a processing chamber and disassociates to deposit the metal component on a substrate while the organic portion of the precursor is exhausted from the chamber.
However, current MOCVD techniques deposit layers at near atmospheric conditions. Layers deposited at near atmospheric conditions generally have less than desirable coverage of sub-micron features formed on a substrate which can lead to void formation in substrate features and possible device failure. Additionally, atmospheric deposited layers generally have high levels of contaminants which detrimentally affect layer properties, such as layer resistivity, and produce layers with less than desirable interlayer bonding and diffusion resistance. Further, atmospheric layer deposition processes have been observed to deposit materials that flake or delaminate from the surfaces of the chamber or substrate and become a particle source within the chamber. Particles can produce layering defects in the deposited layers and result in less than desirable interlayer adhesion.
Additionally, there are few commercially available organometallic precursors for the deposition of metal layers, such as tantalum, niobium, and tungsten precursors by MOCVD techniques. The precursors that are available produce layers which have unacceptable levels of contaminants such as carbon and oxygen, and have less than desirable diffusion resistance, low thermal stability, and undesirable layer characteristics. Further, in some cases, the available precursors used to deposit metal nitride layers produce layers with high resistivity, and in some cases, produce layers that are insulative. The insulative properties of the layer are generally a result of the crystalline structure or the chemical composition of the materials deposited from the precursor. For example, in tantalum layers, as the nitrogen content increases, the layer becomes increasingly resistive. A high nitrogen content can transition a good conducting phase of tantalum nitride with superior barrier properties, such as Ta2N, into an insulating phase, such as Ta3N5. Many of the available tantalum nitride precursors readily deposit an insulating Ta3N5 phase. Contaminants, such as carbon and hydrogen deposited from available precursors can also increase film resistivity. Furthermore, there are no current satisfactory MOCVD techniques and precursors for depositing materials, such as silicon, which can be incorporated in the deposited metal and metal nitride materials to improve diffusion resistance, chemical resistance, thermal stability, or enhance interlayer adhesion.
One additional problem with depositing metal liner layers and metal nitride barrier layers using current CVD deposition techniques is that often during substrate processing, it is required to transfer the substrate between processing chambers or systems in order to deposit both the metal layer and the metal nitride layer. The transfer of substrates between processing chambers and systems increases processing time and decreases substrate throughput while potentially exposing the layers to contamination or to atmospheric conditions where oxidation may occur.
Therefore, there remains a need for a process for forming liner and/or barrier layers of metal or metal nitride materials from organometallic precursors. Ideally, the liner and/or barrier layers deposited are substantially free of contaminants, have reduced layer resistivities, improved interlayer adhesion, improved diffusion resistance, and improved thermal stability than those produced with prior processes. Ideally, the metal and metal nitride layers are deposited at sub-atmospheric pressures.
The invention generally provides an organometallic precursor and a method of forming a metal or metal nitride layer on a substrate by chemical vapor deposition of the organometallic precursor. In one aspect of the invention, a precursor of the formula (Cp(R)n)xM(CO)yxe2x88x92x is used to deposit a metal or metal nitride layer at sub-atmospheric pressures. The method for depositing the metal or metal nitride layer comprises introducing the precursor into a processing chamber, preferably maintained at a pressure of less than about 20 Torr, and disassociating the precursor in the presence of a processing gas to deposit a metal or metal nitride layer. The precursor may be disassociated and deposited by a thermal or plasma-enhanced process. The method may further comprise a step of exposing the deposited layer to a plasma process to remove contaminants, density the layer, and reduce the layer""s resistivity.
The precursor of the formula: (Cp(R)n)xM(CO)yxe2x88x92x, comprises a metal, M, selected from the group of tantalum, niobium, vanadium, and tungsten, having a valence of y, at least one cyclopentadienyl functional group, Cp, which may form between 1 and 5 ligands, x, with the metal, M, and have between 0 and 5 substituents, n, which comprise an organic group, R, and at least one carbonyl group, CO, forming a ligand with the metal, M. The organic group, R, may further comprise one or more carbon silicon bonds, preferably comprising an alkylsilyl functional group. The alkyl silyl group may further include at least one silicon-oxygen bond.
Another aspect of the invention provides a method of depositing a metal layer and a metal nitride layer in situ. The method comprises depositing a metal layer by either a thermal or plasma-enhanced disassociation of a precursor of the formula (Cp(R)n)xM(CO)yxe2x88x92x in the presence of a processing gas, such as an inert gas, a reactive gas, or a combination of both, and depositing the metal nitride layer on the metal layer by the disassociation of a precursor of the formula (Cp(R)n)xM(CO)yxe2x88x92x in the presence of a nitrating processing gas, such as nitrogen (N2) or ammonia (NH3). The metal layer and the metal nitride layer may both be exposed to a plasma following deposition.
Another aspect of the invention provides a method for metallization of a feature on a substrate comprising depositing a dielectric layer on the substrate, etching a pattern into the substrate, depositing a metal layer on the substrate, depositing a metal nitride layer on the metal layer, and depositing a conductive metal layer on the metal nitride layer. The substrate may be optionally exposed to reactive pre-clean comprising a plasma of hydrogen and argon to remove oxide formations on the substrate prior to deposition of the metal nitride layer. The conductive metal is preferably copper and may be deposited by physical vapor deposition, chemical vapor deposition, or electrochemical deposition. The metal layer and the metal nitride layer are deposited by the thermal or plasma enhanced disassociation of an organometallic precursor having the formula (Cp(R)n)xM(CO)yxe2x88x92x in the presence of a processing gas, preferably at a pressure less than about 20 Torr. Once deposited, the metal layer and the metal nitride layer are exposed to a plasma prior to subsequent layer deposition.